The rewards of rooting your phone and installing a custom ROM can be worth the risky, heart-in-mouth process of wiping your mobile's officially sanctioned software. But if you're one of the unlucky few for whom it all goes wrong, leaving you with a £500 paperweight, what do you do next?

While the severity of how badly bricked your phone is varies, the symptoms are often the same -- a reboot loop, switching itself off after the Samsung logo or never getting into the operating system. For the purposes of this article, as long as you can get into recovery mode, there's hope.

I'm going to guide you through the process of recovering a bricked phone and restoring the stock Samsung Galaxy S3 ROM, so nobody will be any the wiser that your phone recently saw its life flashing before its eyes...

1. Wipe the data

The first thing to do is put it into Recovery Mode. You do this by holding down Home, Volume Up and Power. You'll be presented with a menu, which is controlled not by the touchscreen, but by the volume controls and the Menu or Power buttons (depending on the version, trial and error is your friend) to select. So, with that in mind, scroll down to 'wipe data/factory reset'.

Press Menu/Power and you'll be presented with a slightly daunting 'are you sure?' screen, with loads of No options and a single Yes. Scroll to the Yes, then power off your phone with the power button.

2. Source the original firmware and tools of the trade

You may be worrying that you didn't backup the original firmware -- after all, you and your new custom ROM were going to be best buds, right? Not to worry, enough people have been along this road that finding the original firmware online isn't too much of an issue, as long as you can remember which phone model you have. And you should have been made aware of this when you first put a new ROM on your phone.

My test handset is a standard GT-I9300, which is a network-free European model. So, the first step is to track down the corresponding firmware. Samsung-updates.com is our first port of call. Simply find your phone from the drop-down and you'll be presented with a baffling list of seemingly identical firmwares. If you hover above the country code, you'll be able to see which three-letter code applies to you -- BTU is for the UK, so that's what we'll be using. At the time of writing, there's seven with that code, two of them for Android Jelly Bean (which isn't officially available yet), so we'll play it safe and go for this one dated July.

You'll also need Odin, which you should already have if you've managed to brick your phone. It's the tool that allows you to root your phone in the first place. Still, you can download it here if not.

3. Flash the firmware with Odin

Reboot your phone by holding Home, Volume Down and Power. Note that it's Volume Down and not Volume Up like in Step 1. This puts you into download mode, so that the phone is ready to recieve its firmware via USB. The phone will warn you about the dangers of a custom OS, but remember, we're actually putting the official firmware back on, so this scare tactic shouldn't faze you at all.

Back on your computer, unzip the Samsung firmware downloaded in the last step and extract the .md5 file. Open up Odin, and select that .md5 file in the 'PDA' section of Odin. Make sure that Auto Reboot and F. Reset Time is ticked (it was by default for me).

Connect your Galaxy S3 to your computer via the USB lead. Your phone should be detected by Odin -- you can tell when it's happened because a message will pop up in the box at the bottom left (it said '0>